1. Field of the Invention
The present invention relates to an optical recording and reproducing apparatus for effecting the recording, reproduction, erasure, and the like of information by using an optical recording medium such as an optical disk. More particularly, the present invention concerns an optical recording and reproducing apparatus capable of effecting tracking control accurately.
2. Description of the Related Art
Conventionally, as an optical recording and reproducing apparatus of this type, one disclosed in Japanese Utility Model Unexamined Publication No. Sho. 63-55211, for instance, is known. As shown in FIG. 14, this optical recording and reproducing apparatus comprises a movable section 102 having a slider 101 in which an objective lens 100 is incorporated, and a fixed section 105 having a light source 103 and a detecting system 104. The slider 101 incorporating the objective lens 100 is caused to float above the surface of an optical disk 106 by means of a dynamic-pressure air bearing effect, and the distance between the objective lens 100 and the optical disk 106 is held at a substantially fixed value. In this apparatus, a focus control system is adopted in which a focus error occurring due to fluctuations in the amount of floating caused by the surface vibration of the optical disk 106 is corrected by a focusing lens 107 provided in the fixed section 105.
Since the above-described optical recording and reproducing apparatus effects the automatic control of the focus by means of the focusing lens 107 provided in the fixed section, it is unnecessary to dispose an objective lens actuator for effecting the automatic control of the focus on the movable section 102 of an optical head. For this reason, the movable section 102 of the optical head can be made substantially compact and lightweight as compared with a conventional optical head, so that this optical recording and reproducing apparatus offers a promising technology capable of attaining high-speed access.
However, although the above-described optical recording and reproducing apparatus has a unique arrangement concerning the automatic control of the focus as described above, the apparatus adopts a conventional method concerning tracking control, so that the apparatus has the following problem: That is, as shown in FIG. 14, the above-described optical recording and reproducing apparatus has a tracking actuator 108 incorporated in the movable section 102, and this tracking actuator is comprised of a tracking coil 109 disposed on the slider 101 side where the objective lens 100 is incorporated and a permanent magnet 110 disposed on the movable section 102 side. The arrangement provided is such that fine tracking error of the floating-type optical head is corrected by means of the tracking actuator 108 disposed in the movable section 102, and the random access movement of the optical head to a target track is effected by a linear motor 111 for driving the movable section 102 in the radial direction of the optical disk 106.
For that reason, in the above-described floating-type optical head, the tracking actuator 108 comprised of the permanent magnet 110 and the tracking coil 109 needs to be mounted in the movable section 102 which is moved for an accessing operation. Although the movable section 102 is made lightweight as compared with the conventional one, the weight of the optical head increases by a portion corresponding to the weight of the tracking actuator 108. Hence, there has been a problem in that it is impossible to obtain acceleration sufficient for attaining high-speed access.
Therefore, a floating-type optical head which overcomes the problem of the above-described apparatus has been proposed. In the optical head, to attain high-speed access my making the movable section more lightweight and compact, the tracking actuator is removed from the movable section, and all the tracking control is effected by only the linear motor used for an accessing operation (The 36th Meeting of the Japan Society of Applied Physics, 2p-ZB-5, 6 (1989).
This floating-type optical head is arranged such that, as shown in FIG. 15, a movable section 120 is comprised of only a slider 121, an objective lens 122, and a mirror 123, this movable section 120 is connected to a linear motor 124 used for an accessing operation, and a fixed section 125 is comprised of a light source 126, a light detecting system 127, a relay lens 128 for adjusting the focus, and the like. In this head, the focusing control is effected through the following of the surface of a disk 129 by the slider 121 and the driving of the relay lens 128, and the tracking and seeking operations are effected by only the single linear motor 124 for driving the movable section 120.
In the case of the above-described optical head, since it is unnecessary for the tracking actuator to be provided in the movable section 120, so that the movable section 120 can be made substantially lightweight and compact, thereby making it possible to attain high-speed access.
Nevertheless, the above-described optical head has the following problem. That is, since this optical head is so arranged as to effect both the tracking and seeking operations by means of the single linear motor 124, even the fine tracking control for causing the movable section 120 of the optical head to follow one track is inevitably effected by the linear motor 124.
To effect this fine tracking control, however, although it is necessary to control the driving of the linear motor 124 in a high frequency band, the control of the driving of the linear motor 124 in a high frequency band becomes unstable, as shown in FIG. 12, owing to the inertial mass of the movable section 120 and the linear motor 124 itself.
For that reason, in order to ensure stable control of the driving of the linear motor 124 and operate a servo system for controlling the tracking operation stably, it is inevitable to set the frequency band for controlling the tracking servo to a narrow band. As a result, new problems arise in that the response speed of the linear motor 124 becomes slow, and that it is difficult to perform tracking for instantaneously controlling fine deviations in tracking, making it impossible to obtain sufficient tracking accuracy.